1. Field of the Invention
Embodiments of the subject matter disclosed herein generally relate to methods and devices, and more particularly, to mechanisms and techniques for actuating one or more vanes of a variable inlet guide vanes system.
2. Description of the Prior Art
Actuation systems for adjusting guide vanes are used in turbomachinery equipment, including but not limited to compressors, pumps, and expanders. In particular, variable inlet guide vanes (IGV) may be used in compressor applications to adjust an angle of incidence of inlet air into a first compressor rotor and to control an amount of inlet air to ensure proper surge and to maximize efficiency.
The actuation system may be employed e.g., for recovering methane, natural gas, and/or liquefied natural gas (LNG). The recovered gases may originate from jetty pipelines in the form of boil-off gas (BOG). The recovery of such gasses would reduce emissions and reduce flare operations during the loading of LNG onto ships. Other applications of the actuation system are known in the art.
Variable IGV systems provide a compressor with greater capacity control and reduce energy loss by varying the flow and pressure ratio of air and/or fluids into the compressor based on operating conditions. In this regard, it is noted that a compressor should be lightly loaded when started and then progressively loaded as the compressor becomes fully operational. The IGV system contributes to the control of gas flow during these phases. The variable IGV system is arranged at the inlet of the compressor and the vane blades can be rotated about their aerodynamic center to promote swirl. Moreover, by rotating the vane blades to have an optimal incidence angle with the compressor impeller's leading edge, inlet losses can be minimized.
An example of an adjustable IGV system is shown in FIG. 1, which is reproduced from M. Hensges, Simulation and Optimization of an Adjustable Inlet Guide Vane for Industrial Turbo Compressors from the Proceedings of ASME Turbo Expo 2008: Power for Land, Sea and Air (Jun. 9-13, 2008), the entirety of which is hereby incorporated by reference. FIG. 1 illustrates an adjustable IGV actuation system 100 including an actuator lever 102 directly connected to a first vane 104. The first vane 104 is connected via a drive arm 106 to a driving ring 108. The first vane 104 is rotatably attached to a guide vane carrier 110. A plurality of other vanes 112 are rotatably attached to the guide vane carrier 110. The plurality of vanes 112 are actuated by a plurality of linkages 114 that are connected to the driving ring 108. Thus, when the actuator lever 102 is rotated, it determines a rotation of the first vane 104 but also a displacement of the driving ring 108, which results in a movement of the plurality of linkages 114 and a rotation of the plurality of vanes 110.
In operation, when an actuation force is applied to the actuator lever 102, the force is transferred to the driving ring 108 as an asymmetrical force that causes the driving ring 108 to rotate eccentrically. This happens as the plurality of linkages 114 are linked to the driving ring 108 on a single side of the driving ring, which makes the opposite side of the driving ring 108 free of any force, and thus unbalanced. The asymmetrical forces create a bending torque that may cause the vane assembly to deform, making it susceptible to misalignment and vibrations. Additionally, high actuation forces are required in order to drive the actuator lever 102 to rotate the driving ring 108, which exacerbates the bending torque.
Another approach is to have a geared configuration, i.e., a geared mechanism between the driving ring and the guide vane carrier. However, this approach is not favored by the users as it requires high precision machining, a high actuation force and a design that takes into account the changing temperatures of the teeth.
Still another problem observed in the traditional IGVs is the seizing of the adjustable vanes in applications where the vane assembly is subjected to cryogenic temperatures. This happens when a clearance between the driving ring and its housing is small and the thermal expansions of the driving ring and the housing are different.
Yet another problem observed is that the location of the actuator lever 102 on a lateral side of the variable IGV increases the overall width of the assembly making them unsuitable for applications and installation beyond the first stage of a compressor.
Accordingly it would be desirable to provide methods and devices that avoid that aforementioned problems and drawbacks.